1. Field of the Invention
This invention relates, generally, to electrically driven dispensing and aspirating machines.
2. Description of the Prior Art
Thixotropic pastes such as most silicones, polyurethanes, adhesives in general, human and animal fat, and the like, exhibit non-Newtonian, i.e., thixotropic behavior when being dispensed or aspirated. Thus, as indicated in the diagram below, very high pressures are required to produce even low flow rates of such substances. ##STR1##
Hydraulic and pneumatic machines are currently used to dispense thixotropic materials, as well as polymers, pastes, and other high viscosity materials that exhibit non-Newtonian behavior. More particularly, such machines are used to drive pumps and pistons that dispense and meter such materials. However, there are a number of drawbacks with both of these types of machines.
For example, hydraulic machines are heavy, expensive, and somewhat insensitive in that they cannot generally be used to adequately control small volumes and low flow rates. As a result, they are usually used in large systems, i.e., those of five gallons or more.
Pneumatic machines are lighter in weight and less expensive, but due to the compressibility of air they cannot provide consistent repeatability of shot sizes and flow rates. For the same reason, they respond sluggishly to changing demands, i.e., they cannot respond instantaneously to changes in flow rates as required in many applications. Where thixotropic materials are being handled, unacceptably large air cylinders are required to produce even very small deliveries.
What is needed, then, is a revolutionary, entirely new way to dispense and aspirate materials exhibiting high viscosity. Those of ordinary skill in this art, however, are continuing to refine the existing hydraulic and pneumatic systems in the belief that their respective limitations can be overcome if enough refinements can be made.